1. Field of the Invention
The invention relates to a system for measuring the change in position of an aircraft or flight simulator flight controller, with respect to a fixed aircraft or flight simulator reference, resulting from an applied force. More specifically, the invention relates to such a system which incorporates a six-axis force transducer.
2. Description of Prior Art
In order to quantitatively evaluate and/or simulate an aircraft flight control system, force versus position data must be collected throughout the entire excursion authority of all flight controllers of the flight control system. The flight controllers would include, for example, the control column, the aileron wheel, the rudder and toe brake pedals as well as possibly the nosewheel tiller and the throttle levers. This data must be collected under both quasi-static and dynamic conditions. The data must be of an absolute nature giving precise force and position values independent of set-up or operator changes.
One such prior art system for performing the measurements is described in Report No. UA-00-18 of Fokker-VFW B.V., entitled "Fokker Control Force Measurement Equipment Users Manual", and U.S. Pat. No. 4,358,959, Lam et al, Nov. 16, 1982.
The patent teaches a method to measure the parameters of a damped spring supported mass. Included in the patented system is a method of compensation for damping and inertia while performing a measurement so as to reduce the influence of these factors while collecting static data. The system of the patent measures a single force axis which is oriented mechanically as close as possible to a flight controls primary axis. The position sensing employed records a linear position with no calibration or compensation capability.
The system as defined in the Fokker Report suffers from the problems of lack of accuracy, lack of repeatability, operator dependent results, and lack of reliability. These problems result from the following drawbacks:
1. Sensitivity to side loads
A force applied to the load cell in any axis other than the principle axis in the prior art equipment produces a signal which is not representative of the direction or magnitude of the force. The result is a force signal that can be severely corrupted if the operator fails to apply a purely axial force through the load cell.
2. Drift prone position measurement
The position transducer used is actually a velocity transducer, the signal of which is integrated to a position signal. Any offset in the velocity signal or the analog integrator results in a drifting position signal.
3. Linear position measurement
Position signals are strictly straight line positions. This introduces errors when measuring controls which move through an arc (e.g., control column).
4. Analog system
The Fokker system is purely analog making interfacing with digital computers etc. impractical and also requiring frequent re-calibration.